“I’m sorry about what happened yesterday. I…I wasn’t myself.” Those words, or something like them, have been offered countless times as an explanation for (mis)behaviour, but what do they actually mean? People seem to have a sense of an intrinsic self, a personality they identify with, and many people are concerned about how outside factors might (like birth control pills) influence this personality or change the way they behave. In this post, I’d like to explore how we construct and define our sense of self, but rather than writing an essay on the subject, I’m hoping to start a discussion about it.

To help focus the discussion (and because I can’t resist throwing in some exciting biology), let’s talk about parasites. Many parasites can change the behaviour of their host, sometimes quite dramatically. They’re an amazing class of creatures and would easily merit a whole series of blog posts (or a whole book, for that matter). From viruses that invade cells to wasps that lay their eggs in other animals, parasites are ubiquitous and, from our point of view, often rather unusual. I’ll briefly discuss a few examples and then we’ll move on to the main question: How would you feel if you discovered that parasites were part of who you are?

The emerald cockroach wasp is a parasitic wasp that lays its eggs on cockroaches, which serve as a food source for the young. To capture a cockroach, a female wasp stings it twice; the first sting, near the head, stuns the roach and temporarily paralyzes it; this allows the wasp to place the second sting more precisely. By targeting specific nerves with her venom, the wasp blocks the cockroach’s escape reflex, turning it into a docile, sluggish creature. The wasp guides her captive by tugging on its antennae, leading it back to her burrow where she lays an egg on its abdomen. A few days later, the egg hatches into a larva which feasts on the meal left by its mother. Over the next two weeks, it will eat through the insides of the still-living cockroach before making a cocoon inside its victim’s body.

Another example is the famous fungus that turns ants into zombies, using them to spread itself. The fungus takes over the ant’s brain, making it leave the colony and climb up to the underside of a leaf. The ant clamps its jaws down on the leaf, gripping it tightly even as the fungus kills the ant and emerges from its corpse. Gruesome as it may sound, this puts the fungus in an ideal spot to spread its spores — growing in a rich nutrient source high above the forest floor.

A candidate parasite which might dramatically affect the behaviour of humans is the protozoan Toxoplasma gondii. This parasite, which causes toxoplasmosis,divides its life-cycle between two different hosts. T. gondii reproduces sexually in cats, producing spores that are taken up by other warm-blooded animals, mainly rodents such as mice and rats. The spores reproduce asexually in these animals, infecting their tissue; when an infected mouse or rat is eaten by a cat, the cycle starts again. Rats and mice usually try to avoid getting eaten by cats, but T. gondii changes their behaviour to tip the odds in its favour. Infected rodents become less afraid of cats and even seek out places that smell of cat urine. It’s unclear whether T. gondii has similar effects in humans, but Professor Jaroslav Flegr thinks so. In 2001, his research group showed that people infected with T. gondii were more likely to be involved in traffic accidents, probably due to slower reactions. Though he hasn’t been able to prove it yet, Professor Flegr thinks T. gondii might also cause bigger changes in personality, like making people more daring.

So, the question: if you found out that you’ve had a parasite that’s been affecting your behaviour or personality for some time, would you want it removed? Let’s not worry about any health effects; we’ll just assume they’re negligible and focus on the question of identity. To help get you going, here are some specific questions you could think about:

Does it matter what kind of effect the parasite has? What if it made you daring, like T. gondii? How about more energetic? more lethargic?

What about parasites (perhaps an STD?) that made you more sociable, flirtatious or extroverted?

What if it was something minor, like making you favour the warmest spot in the room or prefer not to go outdoors?

Would it make a difference if these changes were because of “your” gut bacteria instead of a parasite?

Does it matter how long you’ve been affected? Would you want to get rid of a parasite that’s been influencing your personality for 5-6 years? 5-6 months? most of your life?

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24 thoughts on “What makes you who you are?”

Very interesting questions, and almost impossible to answer! Just what I like.🙂

We all do seem to have some sense of “self” that is very important to us. This idea isn’t more than an illusion of (non-)control, I think. Many things we perceive are illusions, of course, and some of them might be quite important for us to deal with our daily lives. Some probably lead to less pleasant things, like blaming the hurtful things we do on “just the way we are”.

For me, I think that it would matter what kind of effect the parasite has. Like probably most people, there are parts of my personality that I like more, and some that I like less. If getting rid of a parasite would, for instance, make it easier for me to focus on things, I’m pretty sure I’d be happy to do that, no matter how long it’s been going on for. If the parasite, on the other hand, made it more easy for me to focus, I’d be happy to keep it. I don’t mind that there’s a parasite involved. Of course, changing one part of your personality might have an effect on many other parts.

It’s interesting to think what finding out the effects of parasites on personality could mean for people who are very unhappy with themselves. I could see it becoming a big business – all kinds of drugs, diets and other methods to get rid of parasites that produce an unwanted effect, but maybe also infecting people on purpose to “give” them characteristics they’d like (bravery? sexual activity?). Even if the effect on a single person could be almost anyting, just the fact that on average, a parasite would cause a certain change, could be enough to make it into a huge business.

To answer your first question, and I imagine many people will think similarly, yes, it would certainly matter what kind of effect the parasite would have. Assuming negligible health effects I can see a whole suite of traits that I wouldn’t mind being gifted with. Similarly, there would be other traits that I’d probably not be plagued with (lethargy, indifference… pretty much any negative trait I guess).

For me, an important question that ties in with this would be “how severe are the changes and how noticeable the effects?” I can imagine your surroundings might be quite surprised if your character was to change dramatically suddenly.

Similarly, whether I would mind the duration of infection depends on its nature. If it would suddenly explain why I have been depressed for the last three years I would very much like to be rid of it. Positive traits that turned out to be parasite-induced however and have been with me for a long time I probably would like to keep. Other than most people close to you knowing you as you are now and have been the last few years, these traits might have even gotten you where are now in, for example, your career. Removing this might have unexpected effects on your life.

Another factor to come into play is of course how easy it is to rid yourself of this parasite. If its effects are innocent but a treatment painful, demanding and long-term, many people would probably not bother.

The example you mention of your effects of your gut flora makes me wonder though: who is to say that we aren’t already being influenced by other organisms living inside of us? As Hannele suggested, our sense of self is largely a construct, and you’d like to think that “you” yourself are in control. But what if you aren’t completely? Does your gut flora influence your behaviour? Would it help explain differences in people’s metabolism? This, of course, borders closely on the question how genes affect behaviour, and how much you are in control, and how much your genes are in control. That is a whole topic to itself, so I won’t go there now, but it borders on this.

Lastly, as Hannele points out, the potential for pharmaceutical companies to develop drugs and, possibly, enhancements is there. Maybe the future for mankind is not the bionic man-machine, but the symbiotic man-parasite…

Truly fascinating post! I don’t have much to add to the discussion, except I am still getting used to the idea of being an “ecosystem” rather than a discrete being. As an artist/writer, I absolutely love to ponder ideas like this. I think it’s because the possibilities for exploration and discovery about life seem to grow wider–not narrower– the closer we look.

I have a lot of thoughts too! But I think I would say “no” to removal of anything.

I imagine I’m not alone in feeling that there is a difference between keeping something that you already have, and adding something new. So, if you offered me a parasite that made me hmm, tidier, then i would say no. But if you told me that i already had it, then i would keep it. Perhaps it is a policy of non-intervention? But it isn’t entirely logical to me that these things have different answers.

Perhaps I’d accept some medical treatment (removing, or adding a parasite) if there was something actually wrong with me, so not an inconvenience, but a really really problematic thing. I’m not sure I’d have a parasite removed if it was just, say, making it difficult for me to wake up in the morning. I’d be concerned that it would be part of me. But I suppose if I’d only had it for a week, then it could be removed. If I thought that I could/might feel like I was not me, then I would say no.

I think also that if you chose an “enhancement”, like being a quicker-thinker, then it would just feel like cheating to e.g. get a better degree/job. Just like performance-enhancing drugs in sport. And so I wouldn’t feel like it was me. But if you told me that I had been infected by a parasite as a baby and that why I got a place at oxford, then I really wouldn’t mind, and I wouldn’t feel like it was cheating.

The whole idea of an industry selling these parasites is really rather terrifying. Although if there were something that could help with real, serious problems of mental illness, then i would be in favour of more scientific research on it.

I’m finding it rather tricky to write a non-rambling response to this article – it is too interesting a topic to have a simple opinion!

I think what you are speaking about has far reaching implications that impact our notion of self, but also culture. We are beginning to understand how the microbial biome in humans shifts by contact and by geographic location as well. People living in warmer regions vs. colder, living by the sea and so on and the collective impact of the human microbiome, have a consequental effect on thoughts behaviors and ultimately culture. This influence has no doubt impacted the course of history far more than the crude examples we have previously known of such as the black death. To understand ourselves more fully we must understand these deeper connections we have to the biological functions of our entire ecosystem and not see ourselves in isolation from the context of the rest of the larger body of life. After all, if we go by the numbers even in our own body, we are only 10% human.

Please forgive the lengthy reply. I think this topic is of great importance as far as understanding ourselves and being able to navigate better.
I do not think we need to do more to prove it as much as recognize the value of scientific evidence that already exists without our prejudices blocking our view of what that evidence states. I think the same way astronomy fitfully destroyed the earth centered view of the cosmos, I think biology may be on the verge of fitfully destroying the human centered seat of awareness.
Some common examples of the evidence I am talking about is how rabies does brain surgery on mammals to make then hydrophobic, non fearful, and exhibit sudden aggression.
The biology and physiology of rats is edited by T. gondii,such that they are “romantically” attracted to felines through their urine
Evidence of neurotransmitter excretion by any number of microbes in the intestines is well documented.
The social deficits related to Autism symptoms in rats has been corrected by certain microbes. This clearly links relationships between microbes and complex organism behaviors such as social behaviors.
Barley sends out signals to lady bugs when the plant is under attack by aphids to tell them to come to eat the parasite
The Gallfly hijacks the metabolism of certain trees to create a womb for its eggs to develop.
Even endosymbiotic theory is well established and posits a symbiotic co-evolutionary relationship within cells through organelles such as mitochondria in eukaryotes and chloroform in plants.
Our gut has its own nervous system that is far more geared to communicate outward toward our brain rather than receive information from our brain. This tells me that what we see at the seat of consciousness through our verbal awareness may be an illusion.
If we were to use behaviors as evidence and then put these microbes, plants insects on trial in a human court of law and charge them with the intentional acts they appear to perform – and we did this without the stigma of our existing human centrism biases – I think there is strong evidence of as least the possibility to see that our concept of self and the grandiose hubris we associate with our capacity to use verbal abstract thought processes are extremely overblown. In fact, most if not all of what we think may be a byproduct of some combination of thought processes and actions taken by creatures other than ourselves. We may be missing how this all works because we think that thinking and awareness can only happen the way we happen to think they do. By comparison to other biological forms we are quite weak when we consider the fact that plants, microbes, and animals have been farming us and each other, regulating the atmosphere, and more with techniques that include brain surgery chemical and biological form various breeding tactics and altering metabolism to enhance biome metabolism and homeostasis as well as communication through dance voice, chemical and more for many millions of years. We just crudely figured out a few primitive basics of communication over the past 10,000 or so with our capacity for verbal abstract thought. There may be far more than what we currently see. It all depends on perspective.
Here are a couple things I wrote on the topic.http://thewisdomoflife.wordpress.com/2012/07/24/parasites-of-all-persuasions-still-suck/http://thewisdomoflife.wordpress.com/2012/10/24/awareness-much-more-than-we-think/http://thewisdomoflife.wordpress.com/2012/10/26/what-biology-says-about-cooperation/http://thewisdomoflife.wordpress.com/2012/11/09/if-you-think-youre-what-you-think-you-are-think-again/http://thewisdomoflife.wordpress.com/2013/01/13/a-trail-of-ideas/http://thewisdomoflife.wordpress.com/2013/02/07/intentional-life-is-serious-business-wasps-cockroaches-and-us/
Here are some other useful linkshttp://bioteaching.wordpress.com/2013/02/13/daily-factoid-some-insects-parasitise-plants/

Thanks for your comment! There certainly all kinds of interesting interactions and dependencies in biology; a lot of the writing on Inspiring Science is my attempt to describe the wonderful complexity of the world around us and expose how parochial our view of it often is. A lot of the examples you linked to discuss something similar — our illusory sense of self and the common but misguided perception that we are somehow better than or different from the rest of life on Earth.

It’s easy to think of examples where parasites have an obvious behavioural effect on humans — not only rabies, but also coughing, sneezing, itching, etc. I think it’s likely that some parasites (like T. gondii) can have a more lasting or profound impact, but I haven’t seen any direct evidence for that. I also don’t know of any evidence that these effects have had a major impact on human culture — an impact on a scale similar to the climate or geography. It might seem like those are just logical extensions. If parasites can affect our behaviour in small ways, they can probably also have bigger effects; if they have a bigger effect and vary between populations, they could shape conceivably culture. It’s possible and it’s definitely intriguing, but I try to be cautious about conclusions even they seem logical. I’m the kind of person who wants to see the idea properly and rigorously tested (to the extent we can) — I guess I just feel like our intuition has often led us astray.

Thanks for the interesting links, too; I see that this is something you’ve been thinking about for a while. (I’ve been travelling this weekend so I haven’t had a chance to watch the TED talk, but I’m looking forward to it!) I’m really glad about the response this post has generated and I’m happy to keep discussing!

I completely agree caution is in order when using the necessary tool of inductive reason to explore. Speculation falsely elevated to the status of fact is the issue, not speculation itself. In fact, speculation excluded as a tool when used in the appropriate context also has a stagnating effect on scientific progress. We sometimes artificially exclude ideas as false merely because they are unproven when we need inductive speculation (coupled with reasoned empirical exploration) to expand our horizons. I also think our tendency toward confirmation bias among other things such as pride, prestige and the way livelihoods are sometimes hinged on false or conventional paradigms cloud truth as the center point of scientific and academic focus. Using an oversimplified example;Hippocrates and even more so Galen so powerfully established the idea of humors as the reason for health and illness that it stalled medical progress for well over 1500 years.

As you might imagine, I am really glad for the topic you are dealing with here.

First, I want to say that I completely agree with Hannele, great questions, impossible to answer… But we can still have fun trying…

At this point in time, we are not even you what makes you, “you”. That said, it is pretty safe to start by saying that your brain is what make us whatever we are. That reminds me of the effort to map all the neuronal connections in what they call a “connectome”. It is a good start, but in most versions of the connectome many factors that are not directly related to the actual connections are not accounted for. It is entirely possible that parasites or even our “natural” bacterial or viral companions make substances that affect neurotransmission. As for the question of whether I would change anything, I really don’t know, it depends on what it is. All of us have regreted at one point or another a choice of words or actions. The trick is to figure out what influenced us to make those choices. Sorry for rambling; it’s such an interesting question that I am thinking a million things about it and yet again, am I the one doing the thinking???? (;-)… Thanks for a great post!!!!

I would say the bacteria in our gut definitely influence our thinking at least indirectly — eg, by affecting sugar or nutrient levels in the blood, which has a knock-on effect. It would be interesting to know if they have a more direct impact, too. Maybe it’s time to start taking a more integrative view of our consciousness/sense of self?

Denise, I also feel like this idea has a lot of creative potential. I’m starting to dabble in writing fiction and I couldn’t help but think that it would be great to weave this into a story somehow.

Don’t worry about rambling, Rose; I think that’s an excellent way to respond. I quite liked your “policy of non-intervention”; I feel the same way. Even if it doesn’t seem entirely logically consistent, it certainly feels like there’s a difference between adding something and just continuing as you were. I guess knowing that an aspect of my personality is thanks to some critter or other doesn’t really affect my sense of self, but actually deciding to make a change does. Perhaps it’s because making a choice somehow implies taking responsibility?

For some reason I didn’t think people would care so much whether the change is beneficial or not — I suppose I expected people to be more concerned with the integrity (or not) of their identity than with practicalities. We’ve gotten one clear (sort of) “no” vote from Rose, but I’m actually surprised there hasn’t been a definitive “yes” so far. Nobody out there finds the idea of a microbe shaping their personality to be demeaning or invasive? Or somehow limiting their own autonomy? Actually, that makes me wonder: what if the effects were somewhat unpredictable (as they likely would be)?

I hadn’t thought about the idea of using parasites with the intention of getting an edge, but I guess it’s not that far-fetched. We’ve already got performance-enhancing drugs, so why not performance-enhancing bugs? That’s definitely great fodder for a sci-fi story…

Just to make sure nobody gets misled: I don’t know of any conclusive evidence that parasites or gut bacteria are affecting our behaviour. My gut feeling (!) is that it’s likely; it certainly makes for an interesting “what if” discussion. I’ll have a look for any papers about gut bacteria and mood/personality — I’m sure that would be a good subject for a (follow-up) post!

This comment ended up being much longer than I intended, but hopefully it can serve as a springboard for more discussion. I’m really glad to have gotten people thinking about this and I’m looking forward to hearing more of your thoughts!

Fascinating post and interesting questions. As others before me, it is very difficult to answer.

Here’s my answer:
I immediately thought of aliens. Would it not be horrifying if we were visited by aliens that behaved just like the wasp or fungus in your examples above? Even if the predation was minimal (meaning, they would only infect less than 10% of the population or something), it would be cause for an all out war. So, given our species sociability and the potential to spread the parasite because of that sociability, regardless of whether “you” want it removed or not, it should.

That’s a fun idea; I think it’s already been explored in a couple of sci-fi books & films, but I might have a go at playing with that, too — I do want to try my hand at writing fiction. Thanks for sharing your thoughts!

After discussing a bit with a colleague our probably simple conclusion was simply that parasites and in general ‘foreign’ organisms are distinctly a part of who you are. The fallacy of control is a difficult thing to wrestle with since our world view depends on our ability to justify our actions as our own. But, even without parasites, the question is still a difficult one since what we consider to be our choices are often nothing more than a series of hormonal changes or other variations in our bodies and brains which aren’t being controlled by ‘us’. The idea that “I” decide to do something and therefore “I” am in control of my behavior is sort of a lost cause even _without_ the parasite complication. At the same time, I can’t help but think of everything I do from the perspective of me as a single entity that’s in control. “I” have free will and can chose to do anything I like…An interesting offshoot of the conversation (that might be worthy of a blog post) was about how parasitism and symbiotic relationships play an integral role in evolution? I suppose the classic example is of mitochondria but apparently some light sensitive cellular organisms played a similar role in the development of our eyes? I’d like to learn more about it but as we discussed it the thought came to us that it makes much more sense that humans (or any organism) is a mashup of many other organisms that fused sometime long ago in our past and that this process continues to happen today. Lastly, I was intrigued by the possibility of using parasitic evolutionary models to describe the evolution of musical styles in western culture..but that’s getting a bit silly of course

I haven’t heard about a symbiosis with light-sensitive organisms being involved with the evolution of sight, but I’ll try to remember to look into it. I agree, though, that the role of symbiosis, parasitism, etc, would be a nice topic for a post — there are lots of great ecology & evolution stories to share!

I think your reply gets to the heart of what fascinates me about this question: our illusory, but seemingly essential, sense of an “I”. I don’t have much difficulty changing my notion of self to include an ecosystem — even an ecosystem with parasites — but once you start down that path you end up in a world of grey areas and fuzzy boundaries. Maybe we’re OK with considering a long-term parasite part of our “self” and accepting that its effect on our behaviour is just one factor in who we are…but what if it’s a relatively recent change (say, a parasite we’ve only had for six months)?

I think it’s harder to give a clear answer to these sorts of questions if you put them in the context of personal responsibility. If a person behaves in a strange way because they have a fever, we’re not likely to hold them accountable (with certain limits). What about a longer term parasite or a disease like cancer? At what point do we decide that a change in behaviour/personality is no longer exceptional but just part of who the person is, something they have to deal with and take responsibility for? What makes some things count as “external factors” and others as part of us? Will “temporarily parasitized” ever be an acceptable plea in court?

An interesting example to consider is the Salem witch trials. There are a couple of possible biological explanations for the mass hysteria that afflicted the citizens of Salem, including ergot poisoning, Lyme disease, and encephalitis. Would any of these serve to excuse the mass condemnation and execution of “witches”? What if it hadn’t been a parasite, but some kind of chemical product accidentally released into a community (eg, industrial run-off into the water supply)? Would that change your judgement? Personally, I feel like I would judge people more leniently if they were affected by some biological agent or a chemical, even though that’s not really consistent with my statement that parasites are just part of our “self”.

I’ll be looking forward to your fiction! I just wrote my first book last year and am getting ready for the sequel. It was one of the most thrilling adventures I’ve ever had…diving into a fictional world. Hope you enjoy it, too!